As electronic devices increasingly become portable, advances must be made in energy storage devices to enable such portability. Indeed it is often the case with current electronics technology that the limiting factor to portability of a given device is the size and the weight of the associated energy storage device. Obviously, a small energy storage device may be fabricated for a given electrical device application, but at the cost of energy capacity. Conversely, a large energy storage device yielding long life may be attached to a device, but typically at the expense of size and portability. The result is that either the energy storage device is too bulky, too heavy, or does not last long enough for a given application. Typical energy storage devices used for portable electronics include the electrochemical battery cell, and, increasingly, the electrochemical capacitor.
Electrochemical capacitors are a class of devices characterized by relatively high power densities as compared with conventional battery systems. The charge mechanism of such capacitors is typically the result of primary, secondary, tertiary, and higher order oxidation/reduction reactions between the electrodes and the electrolyte of the capacitor.
Heretofore, such devices have typically been made with electrodes fabricated of relatively exotic, expensive materials such as ruthenium. More recently, conductive polymers such as polyaniline have been explored for use as the electrode in such devices. Conductive polymers have the advantage of being relatively inexpensive as well as easy to fabricate. However, such devices have heretofore been successfully fabricated most easily only on noble metal substrates, such as platinum or gold. Electrochemical deposition of some polymers onto non-noble metals and alloys have been accomplished through the use of initiators such as CuCl.sub.2, MoCl.sub.5, IrCl.sub.6, and PtCl.sub.6. Each of these methods have substantial drawbacks. First, the high cost of noble metals makes the fabrication of such devices economically unattractive. Secondly, researchers have found that the initiators explored heretofore have resulted in deposition processes which are very difficult to control, and which yield poor coating quality, i.e., poor adhesion and high resistance. See Kogan, et al, Electrochemical Synthesis of Polyaniline on Tantalum and Stainless Steel Electrodes, Synthetic Metals, 63 (1994) 153-156, at FIG. 3, which illustrates poor capacitor performance. Further, the initiators are either highly toxic or as expensive as the noble metal substrates.
Accordingly, there is a need for an electrochemical capacitor device which is fabricated of a conductive polymer deposited on an inexpensive substrate, and which demonstrates acceptable device performance. There is a concomitant need for a method for fabricating such devices in an inexpensive, repeatable, manner. To accomplish this, there is a need for new processing techniques which allow for the electrochemical deposition of electrically conductive polymers in an economical manner while overcoming the problems associated with the prior art, namely poor adhesion and high resistance.